1. Field of the Invention
The present invention relates to reflectors, and reflector/light source systems suitable for use in flash devices or other devices requiring a uniform illumination of a target surface.
2. Background
Many devices require a reflector/light source system that (i) provides a uniform illumination of a target surface and (ii) has light rays striking the target surface at a relatively shallow angles and (iii) avoids a lamp interference problem. The lamp interference results when the light rays reflected off the reflector walls pass through the light source or its transparent envelope. This problem is described in the book entitled "The Optical Design of Reflectors" by William B. Elmer, Third Edition, Copyright 1989, by TLA Lightning Consultants, Inc. Salem, Mass., pgs. 178-179.
In theory, a parabolic reflector would provide a collimated light beam to uniformly illuminate a target surface located near the reflector opening, but only if the light source was a point light source located at the reflector's focal point, and only if the reflected light (but no direct light from the light source) reached the target surface. If a lamp of finite size was used as a light source, and the direct light from this lamp was blocked (as shown in FIG. 10), then from a shadow would be cast in the center a target plane. If the direct light from the lamp was not blocked the target plane would not be illuminated uniformly. Instead, the illumination of the target plane would be in the form of a bell-shaped curve, such as the one illustrated in FIG. 11.
Other reflectors have also been designed to provide relatively uniform illumination. Such reflectors are described in the above referenced book and are illustrated in FIG. 62 of this book. In evaluating the uniformity of the illumination the author of the book did not consider that the lamp also directly illuminates the target plane. The author, in his caption to FIG. 62 specifically stated that the contribution from "direct light is! ignored)." If the direct light contribution to total illumination of the target plane is taken into account, the target plane is not illuminated uniformly.
This reference also teaches that hybrid and compound reflectors may be used to provide unusual beams of light. However, none of the hybrid reflectors disclosed and illustrated (see FIGS. 63 and 67) in this book are able to substantially avoid lamp interference problem while providing a uniform illumination of a target surface (when the direct light contribution to the overall target surface illumination is taken into account) and providing light rays that strike the target surface at a relatively shallow angles.
One promising reflector/light source combination for use in flash lamp devices is described in U.S. Pat. No. 5,309,329 by Thiel, et al., assigned to the Eastman Kodak Company. The reflector/light source combination described therein provides 90% or better illumination uniformity.
It is the principal object of the present invention to provide an alternative reflector device that achieves similar or higher illumination uniformity than the uniformity provided by the reflector/lamp combination disclosed in U.S. Pat. No. 5,309,329, that has light rays striking the target surface at a relatively shallow angles and, that greatly minimizes a lamp interference problem.